1. Field of Invention
The invention relates to an accelerometer, and, in particular, to an accelerometer that is manufactured by Micro Electro Mechanical System (MEMS) technology and has the capability of sensing one axis, two axes or three axes acceleration.
2. Related Art
U.S. Pat. No. 6,201,284 discloses an accelerometer which adopts proof masses to detect the acceleration of X, Y and Z axes. The proof mass detecting Z axis acceleration only moves along the Z axis, however, the motion of the proof mass detecting X axis may be coupled from the X and Y axes, and the motion of the proof mass detecting Y axis may be coupled from the X, Y and Z axes. The mechanical coupling in this structure is such that the sensing signals of different axes interfere with each other. The performance is thus affected seriously. The performance also relies on the high aspect ratio manufacturing technology. This is because the signals of the X and Y axes are detected by electrodes, which are co-planar with the proof mass. Only high aspect ratio manufacturing technology may satisfy the requirement of high sensitivity and small distance between the proof masses and the electrodes.
Structure improvements and control methods regarding accelerometers are disclosed in U.S. Pat. Nos. 5,756,901, 5,817,942, 5,900,550, 6,223,598, 5,777,227, 6,128,956, 6,149,190, 5,487,305, and 6,018,998.
The acceleration sensing method in the prior art adopts a co-planar electrode structure, as in U.S. Pat. Nos. 5,756,901, 5,817,942, 5,900,550, and 6,223,598. 5,487,305 has the drawbacks of insufficient intensity of signal sensing and complexity of signal processing circuits. Therefore, there is need for a new accelerometer structure.